Impregnating nonwovens with an alkyl acrylate polymer-carboxylic polymer latex

ABSTRACT

A PROCESS FOR OBTAINING NONWOVEN MATERIALS HAVING IMPROVED PHYSICAL PROPERTIES, ESPECIALLY INTERNAL BOND STRENGTH OR DELAMINATION RESISTANCE AND WET TENSILE STRENGTH, IS PROVIDED. THE NONWOVEN FABRICS AND PAPERS ARE IMPREGNATED WITH AN ALKYL ACRYLATE POLYMER LATEX CONTAINING CARBOXYL FUNCTIONALITY AND EXPOSED TO AMMONIA OR AMINE VAPORS PRIOR TO THE DRYING AND CURING OPERATIONS TO OBTAIN THE IMPROVED PROPERTIES. PAPERS TREATED IN THIS MANNER HAVE SHOWN UP TO A TWO-FOLD INCREASE IN INTERNAL BOND STRENGTH.

United States Patent O 3,788,878 IMPREGNATING NONWOVENS WITH AN ALKYL ACRYLATE POLYMER-CARBOXYLIC POLYMER LATEX George L. Wheelock, Avon Lake, Ohio, assignor to The B. F. Goodrich Company, New York, NY. No Drawing. Continuation-impart of abandoned application Ser. No. 725,152, Apr. 29, 1968. This apphcation July 14, 1972, Ser. No. 272,094

Int. Cl. B44d N48 US. Cl. 117-62.2 12 Claims ABSTRACT OF THE DISCLOSURE A process for obtaining nonwoven materials having improved physical properties, especially internal bond strength or delamination resistance and wet tensile strength, is provided. The nonwoven fabrics and papers are impregnated with an alkyl acrylate polymer latex containing carboxyl functionality and exposed to ammonia or amine vapors prior to the drying and curing operations to obtain the improved properties. Papers treated in this manner have shown up to a two-fold increase in internal bond strength.

CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of my copending application Ser. No. 725,152, filed Apr. 29, 1968, now abandoned.

BACKGROUND OF THE INVENTION Nonwoven fibrous materials, typically formed by randomly depositing individual fibers to form a web and then impregnating the web with a binder to hold the individual fibers together, are recognized as possessing many advantages over conventional woven materials. Such advantages include absence of raveling, smoother surfaces, increased softness, improved hand, greater absorbency, higher loft, and others. Underlying these advantages is the fact that, unlike Woven materials which owe their physical characteristics primarily to the construction of the Weave and are thereby limited for a given'fiber, the properties and characteristics of the nonwoven fabrics may be varied over a wide range with the same fiber simply by varying the bonding agent (binder).

' Although the particular fiber/binder combination and web-type will govern the ultimate physical properties achievable in a nonwoven fabric, the amount of binder taken up by the nonwoven substrate and the uniformity with which the binding agent is dispersed throughout the nonwoven will also be important factors in achieving the optimum properties. If the nonwoven substrate as a whole is deficient in bonding agent or if localized areas are deficient, the physical properties such as wet and dry tensile strengths and especially the internal bond strength (resistance to delamination or splitting) are markedly reduced, in fact, the nonwoven is often rendered useless. This problem of obtaining adequate binder content throughout the nonwoven material is especially significant when using the aqueous emulsion binder systems. These are probably the single most important class of binder because they not only provide nonwoven fabrics having excellent physical properties and wear endurance but also, as a practical matter, they are easily applied to the nonwoven substrate by the use of conventional saturation and spraying techniques. It is sometimes so difficult with these emulsion systems to incorporate sufficient binder to obtain the desired level of physical properties for certain nonwoven applications, that it becomes necessary to re'saturate the nonwoven with latex after drying the first binder solution; but this is not a desirable method.

Efforts to overcome the problem of achieving an acceptable binder content has led to much work, primarily directed to obtaining more efficient latices, that is, improved latex binder systems which permit the use of less bonding agent to develop optimum physical properties in the nonwoven material. Typically, these improved latex binders contain reactive monomers, capable of reacting upon the application of heat, catalysis or other chemical reagents, to form cross-linked polymers.

This approach is not completely satisfactory either since the binders, even though more efiicient, are still susceptible to migration through the nonwoven material. During the drying operation, polymeric binder can migrate to the surface of the nonwoven material with the water and emulsifying agent resulting in a non-uniform distribution of the binder and lowered physical properties. The viscosity of the binder latex can be increased prior to saturation by the addition of thickening agents such as natural gums and pastes, polyvinyl alcohol, and the like, to reduce the tendency of the binder to migrate within the nonwoven material, however, this technique is only partially effective and makes it impossible to achieve uniform saturation of the nonwoven.

SUMMARY OF THE INVENTION I have now developed a process whereby nonwoven materials having markedly improved internal bond nated with an alkyl acrylate polymer latex containing carboxyl functionality which for the purposes of the present invention is obtained by blending together a carboxylcontaining polymer or copolymer latex with the alkyl acrylate polymer latex. The saturated fabric or paper is then exposed to vapors of ammonia or an amine prior to" the drying operation.

The nonwoven materials, both fabrics and papers, obtained by the present process will have markedly increased internal bond strength and delamination resistance over conventionally prepared nonwovens without the ammonia or amine exposure. Resistance to delamination has been increased as much as for some papers. The present process enables us to achieve a more uniform distribution of the binder within the finished nonwoven due to the ammonia or amine exposure prior to heat treatment. It is felt that the in situ thickening of the latex binder prior to the drying step reduces the migration of the polymer toward the surface of the nonwoven as the water is removed .during drying.

DETAILED DESCRIPTION The process of the present invention is applicable to any nonwoven material, that is, the particular fiber used in the make-up of the nonwoven and the thickness of 3 the nonwoven does not limit the application of the present process. This is not to say thatcertain fibers are not more useful for certain nonwoven applications than others, but only that if a fiber has the required specifications to be formed into a nonwoven web or mat then the nonwoven so formed may be treated according to the present process.

Natural fibers such as cotton, wool, silk, sisal, cantala, henequen, hemp, jute, kenaf, sunn and ramie may be used to form the nonwoven web or mat as well as synthetic fibers or filaments. Useful synthetic fibers include: rayon (viscose); cellulose esterssuch as cellulose acetate and cellulose triacetate; proteinaceous fibers such as those manufactured from casein; polyamides (nylons) such as those derived from the condensation of adipic acid and hexamethylenediamine or the self-condensation of caprolactam; polyesters such as polyethylene glycol terephthalate; acrylic fibers containing a minimum of about 85 acrylonitrile with vinyl chloride, vinyl acetate, vinyl pyridene, methacrylonitrile or the like and the so-called modacrylic fibers containing smaller amounts of acrylonitrile; fibers of copolymers of vinyl chloride with vinyl acetate or vinylidene chloride; fibers obtained from the formal derivatives of polyvinyl alcohol; olefin fibers such as polyethylene and polypropylene; and the like.

The process of the present invention is particularly advantageous for use with specialty papers which require the saturation of the paper mat with binders in order to modify the structural properties of the paper. Papers from synthetic fibers and those obtained from blends of natural cellulose and synthetic fibers also may be used.

The nonwoven mat or web may be formed by conventional techniques. For example, for papers they will be formed on a moving fine wire screen from an aqueous suspension of the fibers. When other fibers are to be formed into a nonwoven, depending on the particular fiber or fiber blend being used, whether the fibres are to be orientated or deposited at random, the thickness of the nonwoven, etc., the fibrous web can be formed by carding, garnetting, deposition from an air stream, deposition from solution, deposition from a melt, wetlaying, or the like.

The binders employed for the process of the present invention are aqueous dispersions of alkyl acrylate polymers. The required carboxyl functionality is provided by physically admixing with the alkyl acrylate polymer latex, for example, a carboxyl-containing polymer to the alkyl acrylate polymer latex. The carboxyl group will constitute from about 0.05 to about 25% by weight of the total make-up of the polymeric binder.

The alkyl acrylate polymer binder latices employed are obtained by polymerizing esters of fl-olefinically unsaturated carboxylic acids having the structural formula wherein R is hydrogen, methyl or ethyl group and R represents a hydrocarbon radical containing from- I to 12 carbon atoms. .Representative monomers of the foregoing type include methyl acrylate, ethyl acrylate, the propyl acrylates, the butyl acrylates, the amyl acrylates, the hexyl acrylates, cyclohexyl acrylate, phenyl' acrylate, Z-methylhexyl acrylate, n-octyl acrylate, 2'-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-octyl methacrylate, dodecyl methacrylate and the like. Most preferred are the lower alkyl esters of acrylic and methacrylic acid containing from 4 to 10 carbon atoms.

The polymeric acrylate binders may contain one or more other polymerizable comonomers, preferably vinylidene'm'onomers' containing at least one terminal CH ==C group, interpolymerized with the lower alkyl acrylate monomers. Such polymerizable comonomers may constitute up to about 49.95% by weight of the polymer. Such polymerizable comonomers include the conjugated dienes such as butadiene and isoprene; a-OlCfins such as ethylene, propylene and isobutylene; vinyl aromatics such as styrene, a-methyl styrene, chlorostyrene, vinyl toluene and vinyl naphthalene, vinyl halides such as-vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride wherein R is a hydrogen or an alkyl group containing from 1 to 4 carbon atoms and x is a number from 1 to 4, such as N-methylol acrylamide, N-ethanol acrylamide, N-propanol acrylamide, N-methylol methacrylamide, and N-ethylol methacrylamide, polyfunctional compounds such as methylene-bis-acrylamide, ethylene glycol dimethacrylate, diethyl glycol diacrylate, allyl pentaerithritol and divinyl benzene; haloalkyl and 'cyanoalkyl acrylates, excluding amino 'acrylates and methacrylates, alkoxyalkyl acrylates of the formula wherein R is alkylene radical of 1 to 4 carbon'atoms and R is alkyl radical of 1 to 4 carbon atoms or methoxyethyl acrylate; allyl chloroacetate; vinyl chloroacetate and the like as is known by those skilled in the art. There may be also included one or more a,;9-olefinically unsaturated carboxylic acid monomers containing from 3 to 10 carbon atoms. Representative examples 'of such acid monomers include acrylic acid, methacrylic acid, ethacrylic acid, a-chloroacrylic acid, a-cyanoacrylic acid, crotonic acid, fl-acryloxy propionic acid, hydrosorbic acid, .sorbic acid, a-chlorosorbic acid, cinnamic acid, pstyrylacrylic acid, itaconic acid, citraconic acid, malec acid, fumaric acid, mesaconic acid, glutaconic acid, aconitic acid and the like. The preferred acid monomers are the a,p-monoolefinically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid. Mixtures of one or more of the above-mentioned carboxylic monomers may be employed if desired.

I The polyacrylate binders may beprepared by any 0 the conventional emulsion polymerization techniques; About 50 to 100% of one or more of the above-defined alkyl esters of a,fl-olefinically unsaturated carboxlylic acids may be interpolymerized with up to about 50% by weight of other polymerizable vinylidene amine-free comonomers. The preferred polyacrylate binders useful for the present process will contain about 70 to by weight of the acrylate ester, and up to about 30% by weight of other polymerizable comonomers.

The aqueous medium may be emulsifier free or it may contain a surface active agent. When an emulsifier is used to prepare the polyacrylate binders it may range from as low as about 0.01 up to about 6% or more as 10% by weight based on the total monomers. The emulsifier may be charged at the outset of the polymerization or may be added incrementally or by proportioning throughout the run. Any of the general types of anionic or noniomc emulsifiers may be employed, however, best results are obtained when anionic emulsifiers are used. Typical anionic emulsifiers which may be used include those types known to those skilled in the art, for example, as disclosed beginning on page 102 in J. Van Alphen Rubber Chemicals Elsevier, 1956, for example, the alkali metal or ammonium salts of the sulfates of alcohols containing from 8 to 18 carbon atoms such as, for example, sodium lauryl sulfate, ethanol amine lauryl sulfate and ethyl amine lauryl sulfate; alkali metal and ammonium salts of sulfonated petroleum or paraffin oils; sodium salts of aromatic sulfonic acids such as dodecane-l-sulfonic acid and octadiene-l-sulfonic acid; aralkyl sulfonates such as sodium isopropyl benzene sulfonate and sodium dodecyl benzene sulfonate; alkali metal and ammonium salts of sulfonated dicarboxylic acid esters such as sodium dioctyl sulfosuccinate and disodium N-octadecyl sulfosuccinamate; alkali metal or ammonium salts of the free acids of complex organic monoand diphosphate esters; and the like. Socalled nonionic emulsifiers are octylor nonylphenyl polyethoxyethanol and the like. Preferred as emulsifiers are the alkali metal salts of the aromatic sulfonic acids and the sodium salts of the aralkyl sulfonates of the formula REAr-S0a]lVl+ wherein R is alkyl or alkenyl, having 8 to 20 carbon atoms such as octyl, decyl, dodecyl, alkoxy or ethoxy groups, or aryl such as a phenyl radical of the formula wherein R is H or an aliphatic radical containing 1 to 16 carbon atoms as the butyl, decyl, dodecyl and like alkyl or alkenyl radicals, y is CH or O, and naphthyl Ar is benzyl or naphthyl and M is an alkali metal or NH.,. In addition to the above mentioned emulsifiers it may be desirable and advantageous to add post-polymerization emulsifiers and stabilizers to the polymeric latex binders in order to improve the latex stability if it is to be stored for prolonged periods prior to use. Such post-polymerization emulsifiers may be the same as, or different than, the emulsifier employed in conducting the polymerization, preferably anionic or nonionic surface active agents.

To initiate the polymerization free radical catalysts are employed. The use of such catalysts, although in certain systems not absolutely essential, insure a more uniform and controllable polymerization and a satisfactory polymerization rate. Commonly used free radical initiators include the various peroxygen compounds such as the persulfates, benzoyl peroxide, t-butyl hydroperoxide, and 1- hydroxycyclohexyl hydroperoxide; azo compounds such as azodiisobutyronitrile, and dimethyl azodiisobutyrate; and the like. Especially useful as polymerization initiators are the water-soluble peroxygen compounds such as hydrogen peroxide and the sodium, potassium and ammonium persulfates.

The alkali metal and ammonium persulfate catalysts may be employed by themselves or in activated redox systems. Typical redox systems include the persulfates in combination with: a reducing substance such as a polyhydroxy phenol and an oxidizable sulfur compound such as sodium sulfite or sodium bisulfite, a reducing sugar, a diazomercapto compound, a ferri-cyanide compound, dimethylaminopropionitrile and the like. Heavy metal ions such as silver, cupric, iron, cobalt, nickel and others may also be used to activate persulfate catalyzed polymerizations. In general the amount of free radical initiator employed will range between about 0.1 to 5% based on the weight of the total monomers. The initiator is generally completely charged at the start of the polymerization, however, incremental addition or proportioning of the initiator throughout the polymerization is often desirable.

In conducting the polymerization for the preparation of the acrylate binder latices of the present invention the monomers are typically charged into the polymerization reactor which contains the water and the emulsifying agent. The reactor and its contents are then heated and the polymerization initiator added. The temperature at which the polymerization is conducted is not critical and may range from about -30 C. to about 100 C. or higher. Excellent results, however, have been obtained when the polymerization temperature is maintained between 0 C. and 90 C. Polymerization modifiers such as the primary, secondary and tertiary mercaptans, buflers, electrolytes and the like may also be included in the polymerization.

The present invention finds application particularly where the polyacrylate binders themselves contain insufficient or no carboxyl functionality and would normally be considered ineffective for use in the present process or where more carboxyl functionality is required than is desirable in the polyacrylate binder. These latices are useful when there is added a water-soluble salt of a copolymer obtained by the polymerization of an a,}8-olefinically unsaturated carboxylic acid such as acrylic acid, methacrylic, acid, itaconic acid and the like, with one or more esters of an u,[3-olefinically unsaturated carboxylic acid, all as defined above, or a copolymer of an a,B-o1efinically unsaturated carboxylic acid with a polyalkenyl polyether of a polyhydric alcohol.

Useful copolymer additives of the first type include copolymers readily prepared by those skilled in the art as described in water or solvents as isopropanol containing from about 15 to 70% by weight of methacrylic acid interpolymerized with about 30 to by weight of an ester of an a,,8-olefinically unsaturated carboxylic acid. More preferably, such copolymers will contain about 35 to 65% of the methacrylic acid and about 40 to 65 of an acrylic ester. Up to 50% of the ester may be substituted by one or more vinylidene monomers as described herein. Acrylic esters suitable for the preparation of these copolymers include those derived from alcohols containing from 1 to 8 carbon atoms, preferably with acrylic or methacrylic acid. When the acrylic ester is ethyl acrylate the copolymer will generally contain about 40 to 55% methacrylic acid. When the acrylic ester is methyl acrylate about 35 to 50% by Weight methacrylic acid should be present in the copolymer. Usually the salt will be an alkali metal or ammomum salt. Mixtures of one or more of the acrylic esters may be employed if desired to make up these copolymer add tives. The most efficient copolymers are those contaming about 0.1 to about 0.8% by weight of a monomer capable of cross-linking such as methylene-bis-acrylamide, ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl pentaerythritol, divinyl benzene or the like.

Also useful as additives for use with the polyacrylate binder latices are polymers obtained by the polymerization of an a.fi-olefinically unsaturated carboxylic acid such as acrylic acid, itaconic acid, maleic acid, fumaric acid, or the like, with a polyalkenyl polyether of a polyhydric alcohol, said polyhydric alcohol containing about 4 carbon atoms and at least three hydroxyl groups and said polyether containing more than one alkenyl group per molecule. These are described in detail in U.S. Pat. No. 2,798,053 and the disclosure thereof is incorporated herein.

The polymeric thickeners for purposes of the present invention are blended with the polyacrylate binder latices prior to saturation of the nonwoven. Depending on the carboxyl content of the polymer additive and the desired ditives will vary within wide limits. Generally, the abovedescribed external copolymer thickeners will constitute from about 0.1 to 10% by weight based on the total polymer content of the binder latex and more preferably from about 0.5 to 2.5 by weight.

The present process consists of exposing the nonwoven material which has been saturated with one of the above-mentioned carboxyl-containing polymeric latex binders to the vapors of ammonia or amines. By such ex posure, the latex binder is thickened in situ, thereby reducing the migration of the polymeric binder from the interior regions of the nonwoven toward the surface as the water is removed during the drying operation. Thus, a more uniform distribution of the polymeric binder throughout the nonwoven than was previously possible is achieved. The net result of such treatment is a noticeable improvement in the physical properties of the nonwoven material. The internal bond strength or delamination resistance and generally the tensile strength, especially the wet tensile strength, of the nonwovens are increased by employing the process of the present invention.

To achieve the maximum advantage of this invention, the pH of the polymer latices must be maintained below specific limits during the saturation or impregnation. This insures the complete penetration and uniformity of the binder latex throughout the nonwoven material which is essential to obtain the improved physical properties. Although the pH requirement will vary from one latex to another, depending on the monomers employed and the carboxyl content, to be acceptable for impregnation the pH should preferably be maintained on the acid-side. A neutral or slightly basic latex will give acceptable results in most instances, however. In general, the pH of the carboxyl-containi-ng alkyl acrylate polymer latex will be maintained at about 7.5 or below and more preferably between about 6.5 and 2.5. Excellent results are achieved when latices at the higher pH limits are acidified prior to saturation to achieve a more desirable pH and viscosity. To facilitate the saturation of the nonwoven, the total solids of the latex binder is generally maintained below about 50% and excellent results are obtained with latices containing about to total solids.

A critical feature of the present invention is the exposure of the saturated nonwoven material to ammonia or amine vapors. Although ammonia is generally preferred due to its ready availability, gaseous nature and excellent solubility in the binder latices at the temperatures em ployed, primary, secondary or tertiary aliphatic monoamines may also be employed to give excellent results. Typical amines which can be used may contain up to 12 carbon atoms, however, amines containing up to 6 carbon atoms are generally preferred. Gaseous amines such as methyl amine, ethyl amine, dimethyl amine and trimethyl amine have produced excellent results. The higher molecular weight amines which are normally liquids at room temperature, such as primary amines containing from 3 to 11 carbon atoms and the lower secondary and tertiary amines, which will normally exert an appreciable vapor pressure at room temperature, or slightly above, and are readily soluble in water may also be employed. Generally, the amines useful in the present process should have boiling points less than about 150 C. and more preferably less than 100 C. The ready solubility of the ammonia and amines in water insures that binder latex even in the inner-most regions of the nonwoven will be uniformly acted on, thus rendering in situ thickening of the latex to minimize subsequent binder migration. It is the ability of the ammonia and amines to be instantaneously, or essentially so, taken up by the saturated nonwoven and contact both the interior and surface regions with the same effectiveness, which renders the present process so useful and permits the development of superior physical properties in the nonwovens treated in accordance with the present invention.

Attempts to achiece: this 'uniform' treatment or saturated nonwovens using other techniques were unsuccess+ ful. Either the binder could not uniformly penetratethe nonwoven in the cases where thickening of the binder latex prior to saturation was employed, or when post-, thickening of the binder latex was attempted with agents other than the ammonia or amines of this invention, the initial thickening-occurring at the surface of the ,nonwoven is so pronounced and so rapid that it-impedes further' penetration of the thickening agent'to the interior regions of the nonwoven-and consequently these interior regions are subject to migration of the binder upOH drying.

Exposure of the saturated nonwoven material to the ammonia or amine vapors will .vary depending-on the particular latex binder and thickening agent employed. Contact times will generally be less than about '80 minutes, preferably they will range between-about 2 seconds and 5 minutes. With ammonia and the more volatile amines, contact times between 5 seconds and 1 minute have been successfully employed andfound to impart maximum properties to the curednonwoven material. Once maximum thickening of the binder latex is achieved, additional exposure to the ammoniaor amineswill produce no further improvement in the nonwoven properties. Neither will any detrimental effects be realized from pro-, longed exposure to the ammonia or amine vapors, however.

Exposure to the ammonia or amine is conveniently brought about in a chamber maintained at room temperature or above, such as a gravity oven, wherein a sufficient concentration of the ammonia or aminevapors can be maintained for contact with the saturated nonwoven. Al though the exposure ovens can be maintained at elevated temperatures, these temperatures should generally not exceed 212 F., particularly if long exposure times are employed. Because of the short contact times possible with the present process, the saturated nonwoven may becontinuously passed through the gaseous ammonia or amine to facilitate the exposure step. Such a continuous process would be highly desirable'for large-scale commercial operations. 4

After exposure andthickening with the ammonia or amine, the nonwoven material is then dried and cured. The drying step is normally conducted by passing the nonwoven material through'one-or more ovens or heating chambers maintained at a temperature between about200 and 325 F. The preferred drying temperature will be in the range between about 225 and 275 F. The drying ovens may be maintained at subatmospheric pressure to facilitate theremovalof water if so desired 'Ih e dried nonwoven is then typically passed through one. or more ovens maintained at higher temperatures to effect the cure of the binders employed and develop the ultimate physical characteristics ofthe nonwoven. Such curing ovens are maintained at temperatures between about 250 and 325 1*. preferably between 275 and 300 F. In either the drying operation or the curing step the nonwoven material may be passed through the heating chamber once-or it may be recycled for as. many times as required. The drying and curing need not be distinct steps-depending on-the temperature requirements of the binder it may be desir able to combine them in one operation. H 1 p The following examples serve to illustrate the inven: tion more fully, however, they are not intended to limit its scope. In these examples all parts andpercentages are given on a weight basis unless otherwise indicated.

EXAMPLE I.

A latex of an alkyl acrylate polymer having a carboxylcontaining monomer over-polymerized was prepared for use as a binder for nonwoven materials. The polyme'rlatex was prepared by emulsion polymerizing in 64 parts water containing 0.26 part ammonium persulfate and emulsifier an emulsified monomer mixture comprising 32 parts water, 88.5 parts ethyl acrylate, 2.7 parts acrylonitrile, 1.8 U

parts acrylamide and 1.8 parts N-methylol acrylamide. The polymerization was conducted at 80 C. by meter ng the monomer mixture into the polymerrzer for a period sample which was exposed to ammonia for 3 minutes prior to the cure had a greater resistance to delaminatlon, in fact, the cohesion within the polyester was greater than the adhesion of the Bondex Tape to the polyester saturated fabric and the fabric pulled away from the tape beof about one hour. Near the completion of the metering a 5 mixture of 2.6 parts methacrylic acid, 2.5 parts ethyl fore it delammated. acrylate, 0.8 part methyl methacrylate and 0.005 part EXAMPLE II methylene-bis-acrylamide was charged to the reactor. The An acrylate latex bind like that prepared i Example p lym was then maintained at I and diluted to 25% total solids was used to saturate l0 sentially complete conversion was achieved. The total mil fl t papers The procedures l d f t ti I amount of Water and Sodium lahl'yl Sulfate emulslfier and testing were identical to those previously described. present in the final latex was 98 parts and 0.3 part re- The papers were exposed to methyl-amine vapors fro a spectively. The final latex contained about 50% total 10% aqueous solution of the amine for 3 minutes and Selids. 10 minutes prior to the standard 275 F. cure for 5 min- A Saturation bath Prepared by dllutmg the carboxyl utes. Internal bond strengths are reported in Table II and containing acrylate latex to 25% total solids with water. compared with those obtained without exposure to di. Ten mil uhcoated flat Paper (Paterson Parchment (30') ethylamine and an unsaturated paper control. having a minimum fiber to fiber contact and supported within a Dacron marquisette envelope was then saturated TABLE II by submerging the paper in the latex bath. The excess Paper sample: Internal bond strength binder latex was removed by passing the paper between Unsaturated control unexposed to diethy]. padder squeeze rolls maintained at 20 pounds pressure. amine The Saturated P p was then removed from the marqui' Saturated controlunexposed to diethylamine 20 sette envelope. B-minute exposure to diethylamine 32 Papers saturated in this manner were then exposed to 10.minute exposure of di h l i 34 ammonia vapors for varying time intervals by placing the papers in a warm (60-80 C.) ammonia gravity oven. A EXAMPLE HI fresh Solution of ammonium hydroxide was Placed Acrylic acid was interpolymerized with ethyl acrylate, in 11 P on the floor of the Oven Prior to treating the acrylonitrile and N-methylol acrylamide using a conven- P P Immediately after exposure to the ammonia, the tional emulsion polymerization recipe. The resulting polyp p were dried and cured in e 275 F. air oven for 5 mer contained about 1 part acrylic acid, 94 parts ethyl minutes Physical Properties of these cured p p re acrylate and about 5 parts of acrylonitrile and N-methylol then determined and compared against vthese Obtained acrylamide. The polymer latex after dilution with water with identically saturated papers which were not exposed to about 25 total solids was used as a saturant for paper t a- Table I Sets forth the test feslllts- 35 samples in accordance with the procedure described in Tensile (breaking) Strengths and gation of the Example I. The saturated unexposed control papers cured nonwoven m eri l w r determined in r nc with for 5 minutes at 275 F. had Wet breaking strengths of 27 the ASTM D1117-63 Cut-Strip Method. Sp ns f0 pounds/inch and internal bond strengths of 14 ounces/ use in determining the wet tensile strength were soaked inch. The paper samples which were exposed for 3 minin Water at room temperature 16 hours immediately utes in an ammonia oven after saturation and before the prior to the testing. Solvent tensile strengths were obtained ure sho d a 10% inc e i wet ten ile strengths and after immersion of the nonwoven in perehlel'oethylehe over 50% increase in the internal bond strengths. The for 20 minutes at room temperature Samples "X internal bond strength was 22 ounces/inch. of the nonwoven were sandwiched between two 1%"X6" pieces of Bondex T-7 tape and sealed with the weight of EXAMPLE IV an iron at 275 F. for 30 seconds on a heated plate. The About 00 n f acryhte polymer latex 25% resistance to delamination for fabrics 01' internal bond of Example III containing about 1 part interpolym. strength for p p was then reported as the force (ounces/ erized acrylic acid was blended with 2.5 parts of a waterinch) required to peel the tapes apart when pulled at a soluble ammonium salt of a copolymer of about 70% rate of 12 inches per minute. ethyl acrylate and about 30% mcthacrylic acid to increase TABLE I Ammonia exposure time i Paper properties None 5 sec. 1 min. 3 min. min.

Dry tensile strength (pounds/inch) 61 62 Wet tensile strength (pounds/inch) 16 25 32 30 31 Solvent tensile strength (pounds/ineh)-... 37 "39 Dry elongation (percent) 9 9 Internal bond strength (ounces/inch) 2O 42 39 42 40 1 Reported the average obtained for three samples. 1 Oven maintained at 178 F. I

Papers exposed 3 minutes at 178 F. prior to curing, i.e., having an identical heat history with the samples exposed for 3 minutes in Table -I, developed only about one-half the internal bond strength of samples treated with ammonia. In other words, by treating the nonwoven materials impregnated with acrylate binder latices containing carboxyl functionality with ammonia vapors, I have been able to obtain nonwoven materials having twice the resistance to delamination as conventional saturated nonwovens.

When the above latex was used to saturate a nonwoven polyester fabric and the saturated polyester cured for 5 minutes at 275 (3., the unexposed polyester had a resistance to delamination of 21 ounces/inch. The polyester the overall carboxyl content of the resulting latex. After 3 minutes exposure to ammonia at 178 F. and curing at 275 F. for 5 minutes the wet breaking strength and internal bond strengths were 34 pounds/inch and 35 ounces/inch respectively.

EXAMPLE V the nonwovens were exposedtov ammonia'vapors for 3 minutes at 178 F. and then curedconventionally. The

papers showed a noticeableincrease (29 ounces/inch) in internal bond strength over the saturated papers reported in Example III. EXAMPLE VI An acrylate polymer latex suitable for use as a binder for nonwoven fabrics and'papers but containingflno car,- boxyl functionality was prepared by emulsion polymerizing 93 parts ethyl acrylate, 4 parts methyl methacrylate and 3 parts of a mixture of acrylic amides. The latex containing about 25% total solids was divided into two portions. The first portion was maintained'a's is without any modification while the second portion was blended with a TABLE III 12 reacting 'theimpregnated nonwoven web with ammonia or an aliphatic monoamine containing from 1 to 6 carbon atoms at a temperature lessthan 212 F. forabout 1 second to less than 80 minutes; and (3) heating the impregnated nonwoven web ata temperature between about 200 F. and 325 F. a I

. 2. The'process of claim 1 wherein R is an alkylradical containing 2 to '8- canbon atom's,"in (b) the vinylidene comonomer is-selectedkfrom the group consisting of a .vinyl aromatic, a vinyl or vinylidene halide, a vinyl ester, an ,a,;8-unsaturatednitrile, and an n p-unsaturated amide, and in (B) the u,fi-unsaturated carboxylic acidis selected from the group consisting of acrylic and methacrylic acids.

, 3..;The process of claim z'wherein the latex is maintained at a pH'below 7.5 during impregnation, (2) is from about v2 seconds to less than 5 minutes and (3) is bet-ween:200 F. and 300*. F.

4.: The process-of claim 3 wherein (B) contains from about 15 to 70% by weight of acrylic or methacrylic acid with about 30 to 85% by weight of theester'of an 11,)?- olefinieally unsaturated carboxylicacid.

Paper properties Wet tensile strength Internal bond sti'enth' (pounds/inch) (ounces/inch) N0 NH; exposure Saturant Etihtyl acrylate/methyl methacrylate/acrylic amide copolymer a 8X 100 parts copolymer latex plus 2.5 parts water-soluble acrylate/ methacrylic acid copolymer The above examples illustrate the utility of the present process clearly showing that nonwoven materials saturated with the carboxyl-containing alkyl acrylate polymer latices and exposed to ammonia or amine vapors have markedly improved internal bond strengths or resistance to delamination and also improved wet tensile strengths. That the present process is applicable to both papers and nonwoven fabrics is also shown. The processisfespecially attractive in that only short exposure to ammqnia or amine will render these improvements. It is demonstrated that the exposure to ammonia or amine is critical to obtain the improved properties. Theexamples demonstrate that the present process may be employed with alkyl acrylate binder latices which are blended'with other carboxyl-containing latices to achieve the carboxyl functionality.

I claim:

1. A process for obtaining increased internal bond 3 minutes exposure strength in papers and nonwoven fabrics which comprises:

(1) impregnating a nonwoven web with a mixture'of (A)"- an aqueous carboxyl-containing alkyl acrylate copolymer...

latex, said copolymer comprising from about 50 to.

olefinically unsaturated carboxylic acid having tural formula wherein R is hydrogen or methyl and R is a hydrocarbon radical containing from '1 to 12 carbon atoms polymerized, with up to about 40% by weight (b) of one or more copolymerizable vinylidene monomers having at least one terminal CH =C group and being free of amine groups, with (B) about 0.05 to about 25% by weight of carboxyl groups provided by a polymer of oat?- 3 minutes NH: exposure NH: No NH exposure 5. The process of ,claim 4 wherein the carboxylic acid is methacrylic acid in amountfrom about to 65 by weight with about 40 to 65% by weight of an ester wherein thealkyl .group contains 2 to 4 carbon atoms;

I 6. The process of claim 3 wherein (R) is acopolymer of the carboxylic: acid and a polyalkenyl polyether of-a polyhydric alcohol, said polyhydric alcohol containing about 4 carbon atoms ,and at least three hydroxyl' groups andsaidpolyethcr contains more than one alkenyl group per molecule. a

7. The process of clairn 3-wherein R is an alkyl radical containing from- ,4 to 8 carbon atoms present in amount from about70 to, 95% by weight and there is present from-about 5 to 29% by weight of (b). e

8.'jThe processof claim 7 wherein (b) is at least one of 'acrylonitrile, 'metha'crylo'nitrile, acrylamide, methacrylamide and N-methylol acrylamide.

9. The processf of claimj wherein.(a) .is. greater than "7o%"ilivjifvfv ig it f ethyl 'a crylate, and (b) is about 0.5 1 1, 0 gh jp ficut' of acrylonitrile and less than 5% .total.. .of -acrylamide, met-hacrylamide and N-methylol 99-95% y Weight of (a) one or more esters of an 0143;

the strucacid,.methacrylic.acid and itaconic acid with said ester,

olefinically unsaturated carboxylic acids containing from ,3 to 10 carbon atoms in amounts of at least 15%,by weight and an ester of (a) wherein R is 1 to 8 or a polyalkenyl ether of a polyhydric alcohol, saidllatex containing up to about 6% by weight, based on the total weight of monomers, of a surface active agent selected from the group consisting of anionic or nonionic emulsifiers; (2)

or a polymer ofa-nacid selectedv from thegroup consisting of acrylic acid, methacrylic acid, itaconic acid, maleic acidand fumaric'acid with a polyalkenyl ether of a polyhydricalCbhdl, said polyhydric alcohol containing about '4' carbon atoms and at least three hydroxyl groups, said polyether containing more than one alkenyl group per molecule. 11. A' process" of claim 1 wherein (B) is a copolymer of an mil-olefinically unsaturated carboxylic acid containing -3"to 10 carbon atoms in amounts of at least 15% by weight-and an esterbf '(a)wherein R is 1 to 8 overpolymerized in the presence of (A).

w 12. Theprocess of claimll wherein said car'boxylic acid is. selected from the group consisting of acrylic and methacrylic acid. r

(References on following page) References Cited UNITED STATES PATENTS Berke et a1. '11762.2 Coates 11762.2 Schneider 117-106 Priest et a1. 1-1762.2 Goldstein et a1. 11762 Ullman 117-62 14 3,404,022 10/1968 Chance et a1. 117--62.2 3,472,611 10/1969 Langwell 11762.1 3,483,014 12/1969 Issacs et a1. 11762 MURRAY KATZ, Primary Examiner M. SOFOCLEOUS, Assistant Examiner US. Cl. X. R.

117106 R, 140 A, 155 U A; 34-36 

